Energy conversion device and production method therefor

ABSTRACT

An energy converter according to the present invention includes a heat source (radiator  1 ), which receives externally applied energy and raises its temperature, thereby emitting electromagnetic radiations, and a radiation cut portion (mesh  2 ) for cutting down infrared radiations, of which the wavelengths are longer than a predetermined wavelength. The mesh  2  is a woven or knitted mesh of metal wires. The openings of the woven or knitted mesh have an aperture size that is smaller than the predetermined wavelength.

TECHNICAL FIELD

The present invention relates to an energy converter and a method ofmaking the same, and more particularly relates to an illumination sourcethat can exhibit high luminous efficacy with infrared radiations cutdown.

BACKGROUND ART

One of major obstacles that prevent an artificial light source fromachieving high luminous efficacy is that the light source cannot convertenergy into visible radiation without radiating a lot of infrared rays,of which the wavelengths are too long to sense with human eyes, at theexpense of the visible radiation.

An incandescent lamp needs no ballasts, has a small size and a lightweight, and shows a higher color rendering index than any otherartificial light source. Due to these advantageous features, theincandescent lamp is a light source that is used most broadly worldwide.To increase the radiation efficiency of incandescent lamps, people triedto raise the operating temperature of the radiator or to find a radiatorthat has a small radiation in the infrared range. History teaches usthat a carbon filament as a radiator material for an incandescent lampwas replaced by the currently used tungsten filament as a result ofthose efforts. By using the radiator of tungsten, the radiator couldoperate at a higher temperature than the radiator of any other materialand therefore could reduce the percentage of radiations in the infraredrange.

However, in spite of their efforts, the radiation produced by currentincandescent lamps, using the tungsten filament, in the visiblewavelength range is just 10% of the overall radiations thereof. Themajority of the other radiations are infrared radiations, which accountfor as much as 70% of the overall radiations. Also, the currentincandescent lamps cause a heat conduction due to an enclosed gap or aheat loss of 20% due to convection and have a luminous efficacy of about15 lm/W, which is among the lowest ones in various artificial lightsources. This performance of the incandescent lamps has not beenimproved significantly since 1930's.

Meanwhile, Patent Document No. 1 and other documents disclose atechnique of drastically reducing the infrared radiations produced by aradiator and increasing the luminous efficacy of the lamp significantly.According to this technique, an array of very small cavities functioningas waveguides (which are termed “micro-cavities”) is provided on thesurface of the radiator, thereby cutting down radiations of which thewavelengths exceed a predetermined value (e.g., infrared radiations) andselectively emitting only electromagnetic radiations with thepredetermined wavelength. This patent document describes that cavitieswith a width of about 350 nm and a depth of about 7 μm are arranged atan interval of about 150 nm, thereby cutting down infrared radiations ofwhich the wavelengths exceed about 700 nm. This patent document alsodescribes that the luminous efficacy increases as much as six-fold at anoperating temperature of 2,000 K to 2,100 K.

On the other hand, Patent Document No. 2 discloses a technique ofcutting down the infrared radiations by winding a single metal fine wirearound the filament.

Patent Document No. 1: Japanese Patent Application Laid-Open PublicationNo. 03-102701

Patent Document No. 2: Japanese Patent Application Laid-Open PublicationNo. 04-349338

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

One of the biggest problems of the prior art disclosed in PatentDocument No. 1 is that it is difficult to make such an array ofnanometer-scale cavities on the surface of the radiator from theviewpoint of processing technologies. Another problem is that even ifsuch an array of micro-cavities could be formed successfully on thesurface of the radiator, the cavities could still collapse when operatedat about 1,200 K for just a few minutes, even though the radiator has amelting point higher than 3,000 K. That is to say, according to thisconventional technique, the luminous efficacy of the lamp could not beincreased anymore after the lamp has been operated for only a fewminutes.

On the other hand, according to the conventional technique disclosed inPatent Document No. 2, if the metal fine wire extended due to thermalexpansion when the lamp is operated at a high temperature, then themetal fine wire wound around the filament would have a significantlyincreased pitch. As a result, radiations that have wavelengths exceedingthe predetermined value cannot be cut down constantly.

In order to overcome the problems described above, a primary object ofthe present invention is to provide an energy converter in which a meansfor cutting down those radiations with wavelengths exceeding apredetermined value can operate with good stability even at a hightemperature. Another object of the present invention is to provide anillumination source (typically, an incandescent lamp) that can maintainthe effect of reducing infrared radiations for a long time even whenoperated at a temperature of 2,000 K or more.

DISCLOSURE OF INVENTION

An energy converter according to the present invention includes: a heatsource for emitting electromagnetic radiations; and a radiation cutportion for cutting down infrared radiations, of which the wavelengthsare longer than a predetermined wavelength. The radiation cut portion isa woven or knitted mesh of metal wires, openings of the woven or knittedmesh having an aperture size that is smaller than the predeterminedwavelength.

In one preferred embodiment, the openings have a substantially squareshape, each side of which is shorter than 1 μm.

In another preferred embodiment, the metal wires have a diameter of 2 μmor less.

In another preferred embodiment, the metal wires are made of arefractory material having a melting point higher than 2,000 K.

In another preferred embodiment, the refractory material is at least onematerial selected from the group consisting of tungsten, molybdenum,rhenium, tantalum and compounds thereof.

In another preferred embodiment, the heat source is made of tungsten ora tungsten compound and operates at a temperature of 2,000 K or more.

In another preferred embodiment, the radiation cut portion is a stack ofwoven or knitted metal wire meshes, and the stack of woven or knittedmeshes is thick enough to limit the emission of the electromagneticradiations with the predetermined wavelength.

In another preferred embodiment, the predetermined wavelength is 780 nm.

A method of making an energy converter according to the presentinvention includes the steps of: preparing a heat source that emitselectromagnetic radiations; preparing a radiation cut portion that cutsdown infrared radiations, of which the wavelengths are longer than apredetermined wavelength; and arranging the radiation cut portion suchthat the radiation cut portion faces at least one side of the heatsource, from which the electromagnetic radiations are emitted. Theradiation cut portion is a woven or knitted mesh of metal wires, andopenings of the woven or knitted mesh have an aperture size that issmaller than the predetermined wavelength.

In one preferred embodiment, the step of preparing the radiation cutportion includes the step of processing the metal wires while applyingtensile stress to the wires.

An apparatus according to the present invention includes: one of theenergy converters described above; a translucent bulb for shielding theenergy converter from the air; and means for supplying electrical powerto the heat source included in the energy converter.

In one preferred embodiment, the apparatus functions as an illuminationsource.

A radiation cut member according to the present invention cuts downinfrared radiations, of which the wavelengths are longer than apredetermined wavelength, and is a woven or knitted mesh of metal wires.The openings of the woven or knitted mesh have an aperture size that issmaller than the predetermined wavelength.

Effects of the Invention

According to the present invention, an energy converter, which mayfunction as a filament for an incandescent lamp, for example, includes awoven or knitted metal wire mesh as a radiation cut means for cuttingdown electromagnetic radiations, of which the wavelengths exceed apredetermined wavelength, such that the radiation cut means faces theelectromagnetic radiation emitting side of a heat source. Thus, theinfrared radiations from the heat source can be cut down for a long timeand the ratio of visible radiations to the infrared radiations can beincreased in an incandescent lamp. As a result, a light bulb with highluminous efficacy and practically long life can be provided.

In addition, the radiation cut means is implemented as a woven orknitted mesh of metal wires, and therefore, exhibits good thermalstability. Furthermore, the aperture size of the mesh openings does notchange significantly even if the temperature varies. Consequently, highradiation efficiency can be maintained with good stability.

BEST MODE FOR CARRYING OUT THE INVENTION

First, it will be described with reference to FIGS. 1(a) through 1(c)why when an array of cavities, of which the size is comparable to thewavelengths of visible radiations, is provided on the surface of atungsten filament used in conventional incandescent lamps, thosecavities collapse at an operating temperature that is much lower thanthe melting point of tungsten. FIG. 1(a) is a plan view of aconventional tungsten filament on which an array of micro-cavities isprovided, and FIG. 1(b) is a cross-sectional view thereof.

On the surface of the tungsten filament 10 shown in FIG. 1(a) and 1(b),provided is an array of micro-cavities 12. Each of those micro-cavities12 has an inside diameter of 750 nm and a depth of 7 μm, for example. Itis believed that those micro-cavities collapse mainly because of themigration of tungsten atoms. More specifically, the actual latticestructure of tungsten has a lot of lattice defects (i.e., thearrangement of atoms is out of order at a lot of sites). Due to theselattice defects, the atoms and crystal grains have discontinuous andirregular arrangements and define a random microstructure. Even ifthermal energy that is high enough to vaporize and scatter those atomsor crystals actively is not applied, parts of such a microstructure areconstantly on the move (i.e., diffusing or migrating) so as to have itsstructure stabilized. For example, the grain boundary functions as asort of hinge so to speak, thereby making the crystal grains flow.

Owing to such a phenomenon, when the surface of a metal with very smallunevenness is heated to a high temperature, the atoms will flow tocollapse and flatten the very small unevenness on the metal surface justas the surface of a liquid smoothes down. FIG. 1(c) shows how theunevenness on the surface of the tungsten filament 10 has been smoothedout due to the migration of atoms at a high temperature. The presentinventors discovered and confirmed via experiments that themicro-cavities 12, which had been present on the surface of the tungstenfilament 10, easily collapsed and had their surface smoothed out even atan unexpectedly low temperature (e.g., at a temperature at whichtungsten usually hardly vaporizes).

Particularly when the size of the micro-cavities 12 is approximatelyequal to the wavelengths of visible radiation (on the order ofnanometers), the surface of tungsten flattens easily. This could bebecause those cavities themselves, of which the size is comparable tothe wavelength of visible radiation, may function as tiny unevenstructures that are as small as lattice defects.

For these reasons, even if very small micro-cavities are formed on thesurface of a conventional filament made of tungsten, for example, apractically long life cannot be guaranteed at a normal operatingtemperature.

Next, a radiation cut means for use in the present invention will bedescribed with reference to FIGS. 2(a) and 2(b). FIG. 2(a) is a partialperspective view illustrating an exemplary mesh structure 20, whichfunctions as a radiation cut means according to the present invention.FIG. 2(b) schematically shows the overall orientation direction of metalcrystal grains present in each metal wire 23.

The present inventors discovered and confirmed via experiments that insuch a woven or knitted metal wire mesh 20 made up of very fine metalwires 23, of which the diameter was on the order of the wavelength ofvisible radiation, even if there were some lattice defects in therespective metal wires 23, the mesh structure 20 would hardly collapseat a high temperature exceeding 2,000 K. This should be because eventhough the constituent atoms or crystal grains of the metal wires 23 aregiven huge thermal energy at such a high temperature and migrate, theoverall migration direction will agree with the axial direction (i.e.,the length direction) of the metal wires 23. That is why the meshstructure 20, obtained by weaving or knitting the metal wires 23 so asto define a lot of gaps functioning as micro-cavities, exhibitsextremely high thermal stability. On the other hand, as to the verysmall unevenness provided on the surface of a metal or micropores cutthrough metal foil, the smaller the size, the less resistant to theheat.

As in the mesh structure 20 used in the present invention, the thermalstability could be further increased by the crystal structure of themetal wires 23. Specifically, the metal wires 23 are usually obtained bydrawing its material uniaxially by utilizing the ductility thereof. Whenthe metal is drawn in this manner, the crystal grains will be orientedin the directions pointed by the arrows in FIG. 2(b). As a result, thethermal stability of the metal wires 23 would be further increased.

According to the present invention, the radiation efficiency of anelectromagnetic radiator (heat source) within a particular wavelengthrange is increased by using the mesh structure 20 shown in FIG. 2(a).Thus, a high-efficiency radiator, which guarantees a practically longlife even when operated at a high temperature, can be obtained. Itshould be noted that the mesh structure 20 does not have to have theconfiguration shown in FIG. 2(a). FIG. 3(a) is a plan view of the meshstructure 20 shown in FIG. 2. Alternatively, the metal wires 23 may alsobe woven as shown in FIG. 3(b). There are various methods of weaving orknitting the metal wires 23. And the radiation cut means of the presentinvention may be formed by any known weaving or knitting method.

In either weaving or knitting the metal wires 23 to make the meshstructure 20, the process step of bending the metal wires 23 halfway byutilizing the ductility of the metal wires 23 is repeatedly carried out.Thus, the metal wires 23 can be processed mechanically by using a knownmetal mesh maker.

Hereinafter, preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings. It should benoted that the present invention is in no way limited to the followingillustrative embodiments.

Embodiment 1

First, a first preferred embodiment of an energy converter according tothe present invention will be described with reference to FIG. 4.

The energy converter of this preferred embodiment shown in FIG. 4includes a heat source that emits electromagnetic radiations when heatedto a high temperature (which will be referred to herein as a “radiator1”) and a radiation cut means provided around the radiator 1. In thispreferred embodiment, the structure functioning as the radiation cutmeans is a mesh 2 obtained by weaving tungsten fine wires together.

The radiator 1 is usually preferably made of a material that can be usedas a filament for an incandescent lamp. However, the “radiator” is notlimited herein to the filament that generates heat and emits light in anormal incandescent lamp. Nevertheless, if the energy converter of thepresent invention is used in an illumination source, then the radiatormay be made of a known filament material used in an ordinaryincandescent lamp.

It should be noted that the radiator 1 has the function of raising itstemperature when given some energy (e.g., electrical energy), convertingthat energy into electromagnetic radiations, and then emitting theradiations.

The energy converter of this preferred embodiment includes the mesh 2(to be described more fully below) as a radiation cut means, andtherefore, has the function of cutting down radiations of which thewavelengths are longer than a predetermined wavelength. As a result,radiations, of which the wavelengths are equal to or lower than thepredetermined wavelength, can be emitted more efficiently.

The mesh 2 of this preferred embodiment is arranged so as to surroundthe radiator 1 entirely as shown in FIG. 4. However, the mesh 2 does nothave to cover the radiator 1 fully, but may also be arranged so as toface only a portion of the surface of the radiator 1, from which theelectromagnetic wave to use is radiated. For example, if a plateradiator 1 with a mirrored surface is used, then the mesh 2 may bearranged so as to be opposed to the other surface of the radiator 1.

The radiator 1 may be electrically connected to two stem lines, forexample, which are components of a normal incandescent lamp, and receivethe electrical energy supplied through the lines. When used as anillumination source, the radiator 1 and the mesh 2 are enclosed in atranslucent bulb so as to be shielded from the air (i.e., an oxidizingatmosphere). The radiator 1 is externally supplied with electrical powerby way of a base and the stem lines (current supply means) so as togenerate Joule heat, raise its temperature and emit light. In thispreferred embodiment, the radiator 1 preferably operates at atemperature of 2,000 K or more. The radiator is preferably made oftungsten but may also be made of a tungsten compound or anotherrefractory metal. Furthermore, the radiator does not have to have theshape shown in FIG. 4 but may also have a coiled filament structureadopted in a normal incandescent lamp.

The mesh 2 used in this preferred embodiment is a woven fabric oftungsten wires 3 as shown in FIG. 5. In this preferred embodiment, thetungsten wires 3 have a diameter of about 390 nm and their substantiallysquare openings have an aperture size A of about 390 nm each side. Thoseopenings of the mesh 2 function as waveguides (micro-cavities) with acutoff wavelength of 780 nm that is twice as long as the aperture sizeA.

Supposing tungsten has an electrical resistance of 59.1 μΩ·cm at atemperature of 2,000 K, the skin depth of tungsten at a wavelength of780 nm is 197 nm. Meanwhile, the tungsten wires 3 in the mesh 2 have adiameter of 390 nm. That is why it is possible to avoid an unwantedsituation where a plurality of adjacent openings combines together tomake the mesh function as waveguides with a longer cutoff wavelength. Inthis sense, the respective openings of the mesh 2 may be regarded asfunctioning micro-cavities.

In this preferred embodiment, the mesh 2 with such a configuration isarranged near the radiator 1, and therefore, the infrared radiationswith wavelengths exceeding 780 nm, which have been emitted from theradiator 1 toward the mesh 2, are reflected by the mesh 2. This isbecause the openings (waveguides) of the mesh 2 do not pass radiationmodes, of which the wavelengths are longer than a wavelengthcorresponding to the aperture size of the openings. As a result,radiations (photons) with wavelengths exceeding 780 nm are transmittedthrough only the tungsten wires 3 of the mesh 2. In this preferredembodiment, the openings of the mesh 2 have an aperture ratio of 25%,and therefore, the emissivity of those photons substantially decreasesto 75%. Consequently, the ratio of the infrared radiations to thevisible radiation can be reduced and the radiation efficiency of thevisible radiation can be improved.

As described above, if very small unevenness functioning asmicro-cavities (waveguides) is provided on the surface of the radiator1, then those cavities collapse at a temperature that is much lower thanthe melting point of tungsten. However, by adopting the mesh 2 of thispreferred embodiment, such a problem can be avoided and a long-termstabilized operation is guaranteed even if the operating temperature ishigh.

As also mentioned above, even if an extremely fine wire had latticedefects to make atoms or crystal grains flow so as to stabilize thestructure at a high temperature, the fine wire itself would nevercollapse or disappear because those atoms or crystal grains should flowalong the major axis of the fine wire. That is why the mesh 2 can keepoperating normally for a long time even at a high temperature of 2,000 Kor more.

Thus, according to this preferred embodiment, a higher operatingtemperature is guaranteed compared to the situation where micro-cavitiesare provided on the surface of the heat radiator (see FIG. 1). As aresult, the peak wavelength of usable radiations becomes shorter thanthat defined by the Wien's displacement law and closer to the visiblerange. When used as an illumination source, an energy converterexhibiting such radiation characteristics is expected to achieve higherluminous efficacy and replace conventional incandescent lamps in thenear future.

Also, the mesh 2 consisting of the tungsten wires 3 can also be arrangedin the vicinity of the radiator 1, which is operating at a hightemperature, because the mesh 2 has high thermal resistance.

If the mesh 2 of this preferred embodiment is arranged near the radiator1 with a gap of 1 μm or less provided between them, for example, thenthe radiator I will be sensed as a black body when looked at through theopenings of the mesh 2. Accordingly, if a decreased quantity of infraredradiations is transmitted through the openings of the mesh 2, thenradiations having shorter wavelengths than the infrared radiations willbe transmitted through the openings of the mesh 2 at an increasedemissivity. That is to say, the quantity of visible radiation passingthrough the openings of the mesh 2 increases and the luminous efficacyof the visible radiation improves. For that reason, part or all of themesh 2 may be in contact with the radiator 1.

As described above, the mesh 2 used in this preferred embodiment isobtained by weaving or knitting at least one metal wire. Thus, comparedto the structure disclosed in Japanese Patent Application Laid-OpenPublication No. 04-343381 in which a fine wire is wound around afilament, the aperture size of the openings is less likely to vary withthe temperature.

It should be noted that the openings of the mesh 2 preferably have anaperture size A of 1 μm or less. If the cutoff wavelength exceeded 2 μm,which is twice as long as the aperture size A, then the percentage ofinfrared radiations that can pass the mesh would increase.

If the mesh 2 is arranged in the vicinity of the radiator 1 and if theopenings of the mesh 2 function as a black body, then the emissivity ofradiations with shorter wavelengths than the cutoff wavelength over theentire wavelength range becomes equal to that of the black body (i.e.,with an emissivity approximately equal to one). In that case, theemissivity of normal tungsten in the infrared range is 0.4 where thewavelength is up to 1.5 μm (which will be referred to herein as a“short-wave range”) and 0.2 where the wavelength is 1.5 μm or more(which will be referred to herein as a “long-wave range”). Accordingly,once the black body emissivity (=1) is achieved in both of these ranges,the rate of increase in emissivity in the long-wave range exceeds thatin the short-wave range. Then, the ratio of the infrared radiations tothe visible radiation rather increases, thus decreasing the luminousefficacy unintentionally compared to the situation where no mesh 2 isprovided. This is inferable from the Wien's displacement law that saysthe maximum value of the black body radiation is located near awavelength of 1,500 nm at a temperature of 2,000 K. The lower limit maybe about 380 nm because it is necessary to pass light in the visibleradiation range.

Meanwhile, the metal wire preferably has a diameter of 2 μm or less. Ifa mesh with an aperture size of 1 μm is made up of wires with such adiameter (wire diameter), then the aperture ratio will be 10% and theefficiency can be increased to a practical level.

The metal wire more preferably has a diameter of 780 nm or less. In thatcase, it is expected that photons themselves with wavelengths of 780 nmor more are not so easily absorbed into, or radiated from, the wire. Asa result, the quantity of infrared radiations transmitted through thewire decreases, the ratio of the quantity of infrared radiationstransmitted through the mesh 2 to that of visible radiation alsodecreases, and the luminous efficacy would further increase.

The shortest permissible diameter of the metal wire is set approximatelyequal to the skin depth of the metal used as the material of the wire.The skin depth of tungsten with respect to a wavelength of 780 nm isabout 197 nm. That is why the metal wire preferably has a diameter of atleast about 197 nm.

The material of the metal wire is not limited to tungsten but may alsobe molybdenum, rhenium, tantalum, or a compound thereof.

If the energy converter of the present invention is used as anillumination source that emits light sensible to human eyes, then themetal wire to make the mesh is preferably made of a refractory materialthat has a melting point of at least 2,000 K and that can operate withgood stability at temperatures exceeding 2,000 K. To prevent the colorof the emission of the illumination source from becoming unnaturallyreddish, radiations with short wavelengths of about 400 nm need to beincluded at an appropriate percentage. For that purpose, the heatradiator preferably has an operating temperature of 2,000 K or more.

The mesh functioning as the radiation cut means may be either a wovenmesh or a knitted mesh. The knitted mesh is less likely to come part,and more likely to maintain its original shape, than the woven mesh.

The cross-sectional shape of the metal wire may be either substantiallycircular or substantially square. The surfaces, defining an opening thatfunctions as a waveguide (i.e., the inner walls of the waveguide), areportions of the respective outer surfaces of the metal wires.Accordingly, if the metal wires have substantially square crosssections, then the mesh may be designed such that portions of the metalwires, defining the mesh openings, have a planar shape. The combinedarea of those portions of the metal wires, functioning as the innerwalls of the waveguide, is the greater in metal wires with substantiallysquare cross sections than in metal wires with substantially circularcross sections.

Each of the four side surface portions of the metal wires, functioningas the inner walls of the waveguide, is substantially parallel to itsopposed side surface portion. Thus, as viewed from the surface of theradiator, each mesh opening has a relatively small solid angle. On theother hand, if the metal wires have circular cross sections, each meshopening has a relatively large solid angle as viewed from the surface ofthe radiator. That is why the quantity of radiations leaking through theopenings can be smaller in metal wires with substantially square crosssections than in metal wires with substantially circular cross sections.

Embodiment 2

Hereinafter, a second preferred embodiment of an energy converteraccording to the present invention will be described with reference toFIG. 6.

In the preferred embodiment illustrated in FIG. 6, the radiation cutmeans is implemented as a stack of multiple meshes 2. Each of thesemeshes 2 may have a configuration just as described for the firstpreferred embodiment. In this preferred embodiment, the meshes 2 arestacked one upon the other such that associated openings of all thosemeshes 2 stacked are aligned with each other. In this manner, theopenings functioning as the waveguides (i.e., micro-cavities) can have asubstantially increased depth (i.e., waveguide length). Accordingly,even if the stack of meshes 2 is arranged a little distant from theradiator 1 but if the depth of the openings of the meshes 2 is at least1.5 times as large as the aperture size of the meshes 2, then theemissivity of the visible radiation through the openings of the meshes 2can be increased to that of black body radiation. As a result, theluminous efficacy would increase.

INDUSTRIAL APPLICABILITY

An energy converter according to the present invention is applicable tothe filament portion of an incandescent lamp, for example, for use innot just general households but also shops and headlights of cars aswell. The present invention can also use the radiation in a requiredwavelength range more efficiently without dissipating it in vain, thuscontributing to saving a lot of energy and eventually conserving theglobal environment.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(a) is a top view of a conventional tungsten filament on which anarray of micro-cavities is provided, FIG. 1(b) is a cross-sectional viewthereof, and FIG. 1(c) is a cross-sectional view showing the tungstenfilament on which the micro-cavities have already collapsed.

FIG. 2(a) is a partially enlarged perspective view illustrating anexemplary radiation cut means that an energy converter according to thepresent invention has. FIG. 2(b) schematically shows the overallorientation direction of crystal grains present in each metal wire 23.

FIGS. 3(a) and 3(b) illustrate exemplary radiation cut means (meshes)for an energy converter according to the present invention.

FIG. 4 illustrates a first preferred embodiment of an energy converteraccording to the present invention.

FIG. 5 shows the radiation cut means (mesh) of the first preferredembodiment on a larger scale.

FIG. 6 illustrates a second preferred embodiment of an energy converteraccording to the present invention.

DESCRIPTION OF THE REFERENCE NUMERALS

-   1 radiator-   2 mesh (woven mesh)-   3 tungsten wire-   10 tungsten filament-   12 micro-cavity-   20 mesh structure-   23 metal wire-   25 gap (mesh opening)

1. An energy converter comprising: a heat source for emittingelectromagnetic radiations; and a radiation cut portion for cutting downinfrared radiations, of which the wavelengths are longer than apredetermined wavelength, wherein the radiation cut portion is a wovenor knitted mesh of metal wires, openings of the woven or knitted meshhaving an aperture size that is smaller than the predeterminedwavelength.
 2. The energy converter of claim 1, wherein the openingshave a substantially square shape, each side of which is shorter than 1μm.
 3. The energy converter of claim 1, wherein the metal wires have adiameter of 2 μm or less.
 4. The energy converter of claim 1, whereinthe metal wires are made of a refractory material having a melting pointhigher than 2,000 K.
 5. The energy converter of claim 4, wherein therefractory material is at least one material selected from the groupconsisting of tungsten, molybdenum, rhenium, tantalum and compoundsthereof.
 6. The energy converter of one of claims claim 1, wherein theheat source is made of tungsten or a tungsten compound and operates at atemperature of 2,000 K or more.
 7. The energy converter of claim 1,wherein the radiation cut portion is a stack of woven or knitted metalwire meshes, and wherein the stack of woven or knitted meshes is thickenough to limit the emission of the electromagnetic radiations with thepredetermined wavelength.
 8. The energy converter of one of claims claim1, wherein the predetermined wavelength is 780 nm.
 9. A method of makingan energy converter, the method comprising the steps of: preparing aheat source that emits electromagnetic radiations; preparing a radiationcut portion that cuts down infrared radiations, of which the wavelengthsare longer than a predetermined wavelength; and arranging the radiationcut portion such that the radiation cut portion faces at least one sideof the heat source, from which the electromagnetic radiations areemitted, wherein the radiation cut portion is a woven or knitted mesh ofmetal wires, openings of the woven or knitted mesh having an aperturesize that is smaller than the predetermined wavelength.
 10. The methodof claim 9, wherein the step of preparing the radiation cut portionincludes the step of processing the metal wires while applying tensilestress to the wires.
 11. An apparatus comprising: the energy converterof claim 1; a translucent bulb for shielding the energy converter fromthe air; and means for supplying electrical power to the heat sourceincluded in the energy converter.
 12. The apparatus of claim 11, whereinthe apparatus functions as an illumination source.
 13. A radiation cutmember for cutting down infrared radiations, of which the wavelengthsare longer than a predetermined wavelength, wherein the radiation cutmember is a woven or knitted mesh of metal wires, openings of the wovenor knitted mesh having an aperture size that is smaller than thepredetermined wavelength.